Osteoarthritis (OA), sometimes called degenerative joint disease, is a chronic disorder associated with damage to the articular cartilage and surrounding tissues and characterized by pain, stiffness and loss of function. OA commonly affects the hands, spine, and large weight-bearing joints, such as the hips and knees. OA affects nearly 21 million people in the United States, accounting for 25% of visits to primary care physicians. 80% of US population have radiographic evidence of OA by age 65, and 60% of those are symptomatic. In the United States, hospitalizations for osteoarthritis soared from 322,000 in 1993 to 735,000 in 2006.
Articular cartilage is the smooth white tissue that covers the surface of all the synovial joints in the human body. Its main function is to facilitate the movement of one bone against another. With the coefficient of friction as low as 0.003 and the ability to bear compressive loads as high as 20 MPa, articular cartilage is ideally suited for placement in joints, such as the knee and hip. Articular cartilage is composed mainly of water (70-80% by wet weight). It contains specialized cells called chondrocytes that produce a large amount of extracellular matrix composed of collagen, chondroitin and keratan sulfate proteoglycan. Collagen forms a network of fibrils, which resists the swelling pressure generated by the proteoglycans, thus creating a swollen, hydrated tissue that resists compression. Cartilage is one of the few tissues in the body that does not have its own blood supply. For nutrition and release of waste products chondrocytes depend on diffusion helped by the pumping action generated by compression of the cartilage. Compared to other connective tissues, cartilage grows and repairs more slowly.
In addition to proteins and proteoglycans that comprise the extracellular matrix, the chondrocytes produce the enzymes causing degradation of the matrix. This way the chondrocytes maintain a permanent turnover and rejuvenation of the cartilage.
The chondrocytes and the cartilage matrix change with advancing age. The chondrocytes are responsible for both the production of new matrix proteins and the enzymes related to the cartilage degradation. It is generally accepted that the osteoarthritis process includes alterations in the normal balance between synthesis and degradation of articular cartilage and the subchondral bone. In younger individuals the chondrocytes are capable of the appropriate maintenance of the cartilage tissue and keeping it healthy and functional. But with advancing age, the chondrocytes become incapable of providing adequate repair and the process is tipped towards degeneration.
For many years healthy cartilage tissue not only preserves its integrity and function but also performs a constant remodeling to meet requirements of changing loads on the joints. Multiple regulatory pathways by which chondrocytes in articular cartilage sense and respond to the mechanical stimuli have been discovered in recent studies. One of the pathways is a mechanical one, in which the chondrocytes sense the pressure on the cartilage and respond by gene transcription, translation and post-translational modification of the extracellular matrix. Another pathway is a cellular response to the electrical signals generated by the loaded cartilage tissue. It was discovered that an electric potential appears on a cartilage tissue if it is mechanically stressed. It was shown also, that the electric signal on a loaded cartilage tissue can be produced by two physical phenomena: a piezoelectric effect and a streaming potential.
Piezoelectric effect is the ability of some materials to generate an electric field in response to applied mechanical stress. Piezoelectric effect has been observed in a number of soft and hard tissues (including cartilage and bone) and appears to be associated with the presence of oriented fibrous proteins such as collagen. A deformation of a protein molecule produces asymmetric shift of the opposite electric charges comprising the molecule and results in a macroscopic electric potential on the stressed tissue.
A streaming potential is produced when a liquid is forced to flow through a capillary or porous solids (including cartilage and bone). The streaming potential results from the presence of an electrical double layer at the solid-liquid interface. This electrical double layer is made up of ions of one charge type which are fixed to the surface of the solid and an equal number of mobile ions of the opposite charge which are distributed through the neighboring region of the liquid phase. A mechanical stress applied to such a system creates a flow of the mobile ions with respect to the fixed ions on the solid which constitutes an electric current. The electric potential on the tissue generated by this current is called a streaming potential.
Whatever the relative contribution of these two mechanisms is in the electric signal on the stressed tissue, a substantial electric potential is created across the loaded cartilage. It has been suggested that this stress-generated potential (SGP) may play a significant role in cartilage growth, repair, and remodeling. Moreover, because SGP provides a link between physiology and physics it may open a new opportunity of influencing biological processes in the articular cartilage. It has been proven by numerous studies that increase in chondrocytes cell division and the collagen and proteoglycan synthesis are possible and may be achieved in vivo by applying electric potential to the cartilage. This can be done with relatively simple medical devices. In the future these devices promise to become a new non-invasive modality of treatment of arthritis and other cartilage diseases.
Currently available treatment options for osteoarthritis focus on symptoms relief, whereas truly disease-modifying agents are lacking. Thus, the basic therapy includes common analgesics, non-steroidal anti-inflammatory drugs (NSAID), physical therapy and eventually, in severe cases, joint replacement surgery. Conventionally, physicians treat patients exhibiting symptomatic osteoarthritis by the administration of a NSAID. Many such non-steroidal anti-inflammatory drugs are known and are often effective in reducing the symptoms of osteoarthritis. NSAIDs have demonstrated ability to relieve pain, improve activity level, and in some cases improve function of the arthritic joints. None of these drugs, however, have been proven in carefully controlled clinical trials to reverse the long term natural history of osteoarthritis. Moreover, while many of these drugs have demonstrated effectiveness in treating the symptoms of osteoarthritis, they also have been associated with significant toxicities and other risks, such as deleterious effects on cartilage when used over prolonged periods of time. Moreover, in addition to NSAID being very expensive, the toxicities of these drugs limit their usefulness, particularly in elderly patients. Side effects from NSAIDs could be severe; they cause over 20,000 deaths annually in US.
Appropriate exercises, including stretching, strengthening, and postural exercises help maintain healthy cartilage, increase joint's range of motion and strengthen surrounding muscles so that they can absorb stress better. Exercises can sometimes stop or even reverse osteoarthritis of the hips and knees.
Heat Therapy: Heat increases blood flow and makes connective tissue more flexible. It temporarily blocks pain, helps reduce inflammation, stiffness, and improves range of motion. Heat may be applied to the body surface or to deep tissues. Hot packs, infrared heat and hydrotherapy provide surface heat. Electric currents or ultrasound generate heat in deep tissues. Research shows that heat disrupts the body's usual pain cycle by stimulating heat sensors and preventing sensation of pain from reaching the brain. Because the cartilage tissue does not have its own pain receptors, sensation of pain in affected joints comes from underlying bones which are rich in pain receptors. Namely these receptors are blocked by the heat. As of today, there is no direct evidence that the heat therapy itself can reverse or even slow down degeneration of the cartilage affected by arthritis.
Pulsed Electromagnetic Field (PEMF) therapy is known for several decades. It started from observations made by several researchers in seventies decade of the last century that the pulsed magnetic field had a positive effect on healing bone fractures and damaged cartilages. At that time many researches believed that the healing effect was produced by the magnetic field itself and many PEMF applicators with different temporal and spatial patterns of applied magnetic field were claimed as beneficial and patented. The differences between the patented features in the designs of the applicators and methods of treatment were in the amplitudes, lengths of magnetic pulses, their shapes, mainly rectangular and sinusoidal, repetition rates (frequencies), geometry and electrical parameters of the coils. Also, a lot of efforts and creativity were directed to the ergonomics of the PEMF applicators and methods of their positioning near or securing to the human body. It was perceived then that the most important therapeutic parameter of the system was the amplitude of the magnetic field, so the coils were built with high numbers of turns and the pulsed magnetic fields up to hundreds of Gauss were generated.
Alternating electrical fields for the same purpose of bone fracture healing and treatment of damaged cartilages were exploited by several research groups in laboratory studies and clinical trials. Even though the electrical field applicators in these studies proved to be therapeutically effective they revealed a serious drawback—necessity to implant electrodes into the vicinity of the treatment area or at least apply electrodes from outside the body with electrically intimate contact to the skin. In comparison with the electrical systems the PEMF applicators have advantage of not only being non invasive, but also not requiring an intimate electrical contact with the skin. Contrary to the electric field, magnetic field at the employed frequencies easily penetrates the human body practically to any depth.
In an electric field stimulation system developed by Brighton et all (U.S. Pat. No. 7,158,835 B2 and others of the same inventor) a sinusoidal frequency of 60 kHz was employed. This relatively high frequency allowed achieving good capacitance coupling of the treatment volume of the joint with the electrodes at the skin adjacent to the joint. Clinical success of the 60 kHz system proved that the stimulating effect on the cartilage can be achieved with much higher frequencies then tens or hundreds of Hz. It can be expected that the therapeutic effect of the electric fields on cartilage and bone healing exists in a frequency range from a fraction of Hz to up to about one megahertz. One megahertz seems to be a reasonable limit because, as it is known in the art, above one megahertz electric fields in biological tissues produce mainly thermal effects and do not cause biochemical phenomena.
Now it is common knowledge among researchers that the active agent of the PEMF systems is the electric field. Namely electric field interacts with biological tissues, not the magnetic field. From general theory of electromagnetic field it is known that an electric field accompanies every change in time of the magnetic field. Being more specific, the electric field E, created by varying magnetic field, is directly proportional to the time derivative of the magnetic inductance B. The energy associated with the electric field also comes from the magnetic field. It should be noted that the electric field created by a changing magnetic field has one significant difference from the electric field created by electric charges at rest (electrostatic fields): it is a curly field, not potential as the field produced by the electric charges. Contrary to the potential field, in which the field lines begin on positive charges and terminate on the negative charges, the field lines of the curl electric field are continuous; they form close loops, very much as the magnetic field lines around a wire with an electric current. This nature of the curly electric field imposes some limitations on the way the devices, whose intended use is the application of the electric field to human body, should be built. One of these limitations is the presence of areas with very low electric fields, “dead zones”. The dead zones are located near the axes of the electromagnetic coils and produce no therapeutic effect on the treated tissue. In details they will be discussed further herein.
In U.S. Pat. No. 5,842,966 issued to Markoll a method for treatment of arthritis is disclosed. The method involves treating organs by applying a magnetic field by means of an annular coil surrounding the organ, the coil being energized by a pure DC voltage having a rectangular wave form pulsing at the rate of 1-30 CPS. The invention also includes an apparatus comprising a body support encompassed by an annular coil energized as above. The coil is mounted on a carriage running on tracks adjacent the body support. This disclosed device and method has a dead zone along the center axis of the coil.
In U.S. Pat. No. 7,158,835 B2 issued to Brighton et al, a PEMF device is disclosed for preventing and treating osteoporosis, hip and spine fractures, or spine fusions by incorporating a conductive coil into a garment adapted to be worn adjacent to a treatment area and applying an electrical signal to the coil to produce a magnetic flux that penetrates the treatment area and produces an electric field in the bones and the treatment area. The disclosed device has dead zones along the center axes of the coils. The device does not include any heating means.
In U.S. Pat. No. 6,701,185 issued to Burnett et al, an apparatus for electromagnetic stimulation of nerve, muscle, and body tissues is disclosed. The apparatus is comprised of a plurality of overlapping coils which are able to be independently energized in a predetermined sequence such that each coil will generate its own independent electromagnetic field and significantly increase the adjacent field. The coils are co-planar and are disposed in an ergonomic body wrap, which is properly marked to permit an unskilled patient to locate the body wrap, on a particular part of the body, of the patient so that the stimulation coils will maximize the electromagnetic stimulation on the selected nerves, muscles, and/or body tissues near the treated area. The device can be used to treat medical conditions including: muscular atrophy, neuropathic bladder and bowel, musculoskeletal pain, arthritis, as well as possible future applications in the prevention of deep vein thrombosis and weight reduction. This PEMF device has much more uniform electrical field than a simple coil and does not have dead zones. The device does not have a heating element and does not provide PEMF treatment at elevated temperatures.
In U.S. Pat. No. 6,179,772 issued to Blackwell a portable electronic PEMF apparatus is disclosed. The apparatus comprises a PEMF coil, power supply, and electronic switching means. The power supply along with the switching means provide periodic electric power to the PEMF coil. The PEMF coil comprises multiple turns of a conductive wire around a core. The core comprises a magnetic shield layer of materials such as mu metal or soft iron. The power supply comprises a battery, a regulated voltage source and unregulated voltage source from the battery and electronic switching circuit. The electronic switching circuit is tuned to periodically provide power to the coil at a frequency to generate a non-inverting, varying electromagnetic field from the coil. Disclosed apparatus also comprises a heating means. This heating means that provides heat to a body part under treatment is an electric resistive heater, or, in another implementation, a chemical heater. In both cased the applied heat is not regulated and the temperature of the treatment area is not controlled.
In a patent application US 20080288035 filed by Jagjit et al, a stimulation device for treating osteoarthritis is disclosed. The device is intended for therapeutic treatment to a body part such as a joint to promote healing of the body part. It comprises a signal generator for generating a pulsed electromagnetic field based upon a selected treatment mode, a controller for storing the treatment mode and communicating the treatment mode to the signal generator, a heat source configured to provide thermal therapy to the body part, and monitoring means for monitoring the electromagnetic field generated by the electromagnetic stimulating means. Disclosed device uses a heat or cold source to block pain. The cold and heat sources, mainly chemical in nature, are not controlled by any means; they have drifting temperatures and do not provide PEMF therapy in the optimal range of temperatures for osteoarthritis treatment.
As noted in the above discussion, drawbacks of the existing PEMF systems include: not efficient production of the electric field; not uniform coverage of the treatment zone with the electric field, presence of dead zones. As it will be discussed further herein, from the stand point of arthritis treatment, the PEMF systems that provide therapy at ambient temperatures or use uncontrolled heating and/or cooling of the joint do not take advantage of providing treatment at the optimal range of temperatures for the cartilage treatment. Therefore, there is a need for an improved device and method for treating OA that remedy the drawbacks of the prior art treatment devices and methods.